Portable telephones, particularly in the form of current cellular telephones, are well known. In addition, several companies have disclosed and are proceeding with plans for a network of low-orbiting satellites which will allow communication from portable telephones from almost anywhere in the world, without relying on the multiple call regions or "cells" in a cellular telephone system. Portable devices which allow a user to determine their location particularly based on various satellite positioning systems, are also now known. Such systems are generally referred to as Global Positioning Systems ("GPS"). These systems use signals from a series of satellites which allow a portable receiver (i.e. a GPS receiver) on earth to determine its position with a fairly high degree of accuracy.
It is often desirable for one individual to know the location of another. It would be desirable if a first person can conveniently find the location of a second person who might be carrying a portable telephone, without the first person having to call the second person on the portable telephone and interrupt the second person. For example, the second person might be in a meeting and would not consider it convenient to even have a first person call them just to ask where they are, although they might still like to receive on their portable telephone calls for other purposes. Of course, the second person would have no way of knowing whether a call to their portable telephone was for some important reason (e.g. a business call) or just a call from a relative or friend to ask where they are and when they might be home.